1. Field of the Invention
This invention relates to chemical vapor deposition of copper and, more specifically, to such chemical vapor deposition
2. Brief Description of the Prior Art
Aluminum has been widely used as the metallic material for gates and interconnects for most integrated circuits. However, as the feature dimensions of electronic devices continue to decrease, the metallic material requires continually higher electrical conductivity and better resistivity to the electromigration problem than is presently available with aluminum. Copper has been widely considered as a good new material to meet these requirements because it ha higher conductivity and lower resistivity than does aluminum.
Copper films can be grown by either electroplating, electroless plating, sputtering or chemical vapor deposition (CVD). Films formed by chemical vapor deposition usually have better conformity than those formed by sputtering and less contamination problems than those formed by wet processing methods.
Copper hexafluoroacetylacetonate (referred to hereinafter as Cu(hfac).sub.2) and hydrogen have been used as the reaction agents during copper CVD as set forth in an article of N. Awaya et al., "Selective Chemical Vapor Deposition of Copper", Proceedings of VLSI Symposium, Kyoto, May 1989, page 103. When the sample temperature was 250.degree. to 400.degree. C., copper was deposited on metals and metal silicides while no copper nuclei were observed on SiO.sub.2 or Si.sub.3 N.sub.4.
Copper(II) hexafluoroacetylacetonate and alcohols have been used to produce metallic copper. This has been reported in an article of H. D. Gafney et al., "Photochemical Reactions of Copper (II)-1,3-diketonate complexes", Journal of the American Chemical Society, 93 (1971), pg. 1623. In this article, Cu(hfac).sub.2 and several other copper chelates were irradiated by 254 nm UV light in various alcohol "solutions". Copper metal is produced in the solutions. This study focuses on the photochemical effects of the copper chelates. Although the quantum yield was found to be temperature dependent from 3.degree. to 26.degree. C., it was explained by the assumption that a thermal reaction was involved in the reaction mechanism after UV photons created an intermediate to form copper. Because the reaction temperature was so low (3.degree. to 26.degree. C.), the possibility of a completely thermal-driven reaction was not considered.
In an article of F. A. Houle et al, "Surface Processes Leading to Carbon Contamination of Photochemically Deposited Copper Films", Journal of Vacuum Science Technology, A4 (1986), page 2452, bis-(1,1,1,5,5,5-hexafluoropentanedionate) copper (II), which is another name for Cu(hfac).sub.2, and its ethanolate were used to grow copper using either an argon ion laser (257 nm), a KrF laser (248 nm) or a mercury arc lamp. Copper purity was improved when ethanol was used.
In the above described Gafney and Houle articles, the UV photons did not raise the substrate temperature enough to induce a thermal reaction. Furthermore, the use of ultraviolet photons to initiate the copper deposition reaction is relatively inefficient, requires a relatively high surface temperature on the surface on which deposition is to take place and requires a window in the reaction chamber for passage of ultraviolet light into the reaction chamber whereon copper will deposit. This requires periodic cleaning of the window in order to permit the ultraviolet light to penetrate therethrough, this requiring a periodic shut down of the deposition equipment with attendant economic penalties attached thereto.